The invention relates to a method and apparatus useful for the preparation of multiple gauge metal strip by an operation comprising a draw-shaving operation and a drawing operation employing hydrodynamic lubrication.
In many applications, such as the production of copper alloy strip for the formation of electrical connectors and the like, it is necessary to provide a multiple gauge thickness in the metal strip. Heretofore, such conventional procedures as continuous milling have beem employed to produce the desired variations in gauge. Such processes suffer from the disadvantages of being time-consuming and generating an unfavorable form of scrap.
Another procedure which has been investigated in the art comprises the reduction to gauge by a rolling operation. Rolling operations in production are unfavorably restricted to certain shapes, tend to involve complex and costly tooling and are not good enough to provide products meeting commercial tolerances and that are free from structural defects.
Another approach to metal reduction which has been investigated is the combination of shaving followed by drawing as disclosed in U.S. Pat. No. 3,055,102 to Shaw et al. In Shaw et al., a workpiece is reduced uniformly along its entire surface area by a method which employs a tool combining a 360.degree. cutting head mounted ahead of a drawing or extrusion die, between which is provided a channel for the introduction of a lubricating fluid into contact with the workpiece. Shaw et al. suggest that the fluid is employed to minimize or eliminate chatter or wandering of the workpiece during the combined operation, and in that connection, is preferably maintained under pressure while in contact with the workpiece.
Though Shaw et al. deal with a combined process, certain deficiencies exist in its application to multiple gauge metal strip. Specifically, the application of shaving force against only a portion of the total surface of the workpiece would magnify the problems which Shaw et al. sought to remedy in such a manner and at such a degree that the solution proposed in the patent would prove inadequate. The chatter and uneven surface would not be effectively prevented by the employment of the pressurized fluid in contact with the workpiece exiting the shaving tool cutting edge.
With respect to the application of drawing to the preparation of multiple gauge metal strip, certain complications result from the tendency of conventional metal flow. That is, in the normal drawing process, reduction of the thickness in a section results in an increase in section length, so that if the thickness of a given shape varies across its width, the drawing process will result in variable changes in length causing non-uniform metal flow and stresses leading to buckling, twisting, tearing and fracture of the workpiece. Though a wide variety of drawing techniques are known, including the employment of the hydrodynamic principal, none have been suggested or would appear to alleviate the aforenoted deficiencies associated with the drawing of complex multiple gauge configurations. Referring specifically to Shaw et al., the drawing die illustrated therein would be uncapable of controlling the above-noted tendencies while simultaneously attempting to prevent the occurrence of wandering and chatter resulting from the shaving process.
Thus, the individual difficulties recognized with respect to shaving and drawing techniques as applied to multiple gauge strip would appear to be magnified rather than reduced by the application of the method and apparatus of Shaw et al. Moreover, the individual known techniques of shaving and hydrodynamic drawing would appear to offer little if any alleviation of the aforenoted problems and would not suggest the method and apparatus employed herein.